1) Field of the Invention
The invention relates to measuring a physical object, such as fibers as used in pulp and paper processes, from an image consisting of a pixel matrix.
2) Description of Related Art
In the fiber processes employed in the paper industry, for example, the average length of fibers and the fiber length distribution are often highly relevant parameters. One way of measuring these variables is to image a low-density fiber suspension where fibers are dispersed into water functioning as the medium and try to determine a representative number of sample fibers from the fiber pulp by an automatic image processing device to find out the pulp characteristics. In addition to fibers, dimensions of other particles may also be determined.
The measurement is usually carried out in a narrow capillary tube or in a planar measurement cell, which spreads the sample pulp to be measured into a two-dimensional mat. In the capillary tube, the particles to be measured pass by the imaging camera one after another. In the planar measurement cell, a large number of particles to be measured are imaged simultaneously. Representativeness can be achieved by measuring a sufficiently large number of particles.
A problem associated with the above-mentioned solutions is that the accuracy of dimension measurement is determined in the automatic image processing device by the pixel size of the pixel matrix functioning as the detector. The particle dimension will be the multiple of the pixel diameter in the measurement direction. If, in that case, the diameter of the particle image on the detector is sufficient for covering only a few pixels, the measurement accuracy is low (the error may be tens of percents). The success of zooming also affects the accuracy, which will be poor when particles large in proportion to the pixel size are imaged. The fuzziness of the image may result from inadequate zooming or from the fact that an accurate image of the fiber inside the medium is unobtainable due to optical interference.